This invention relates to booms, and more paticularly, to a modular-type boom adapted for use on dragline excavators, cranes and similar machines.
Booms for large material handling apparatus, such as dragline excavators, are subjected to high compression, tension and torsion loading. In booms of lattice type construction, the main longitudinal members are commonly called chords, and these members absorb the bulk of the compression and tension loads applied to the boom. The chords are connected to one another by a series of transversely extending lacings, or struts which lend lateral strength to the boom to resist transverse loads as occur when swinging the boom. A boom of such structure may run as long as 335 feet in length and be at least 21 feet in width along the major part of its length. Booms having such large dimensions cannot readily be shipped by conventional means, such as rail or truck because they are too long and too wide. As a result, the construction of these large booms has normally occurred in the field, and requires a considerable amount of welding at the job sites which requires substantial erection time for the boom.
The inability to ship large booms, and the resulting great amount of field time necessary for erecting such booms results in high costs, and makes it desirable to have a modular-type boom made of prefabricated subsections that may be readily shipped, and then easily assembled in the field. This would not only minimize the amount of welding that takes place in the field, but also reduce the erection time of these booms.
It is common in the art to provide booms comprised of sections that can be joined together in the field. These sections, however, are only longitudinal divisions along the boom, and each section has a width the same as the full boom width. They do not, when unassembled, reduce the width of the boom parts so that they can be shipped intact. This type of segmented boom construction is used for construction type cranes, such as truck mounted cranes, that are used at building sites. They are smaller than large dragline booms used in open pit or surface mining, and their form of construction does not have application to these larger excavators.
Some large booms for excavators may have twin columns that are transversely separated along a part of their length, as shown in Hedeen, U.S. Pat. No. 3,249,238 issued May 3, 1966. This type of boom, however, is assembled from parts by welding at the job site, and the transverse separation of twin columns does not provide any reduction in size that affords transport for boom subsections that can be readily assembled and disassembled in the field by the bolting together of the subsections.